Digital-to-analog conversion for audio applications is performed by generating an output analog signal as the sum, at each sampling instant, of a given number of elementary quantities or contributions. The elementary quantities may comprise, for example, currents supplied by elementary current generators or generated by resistors, or charge stored in capacitors. Digital-to-analog conversion can be roughly divided in two major categories according to the approach adopted in the conversion, i.e. namely either “thermometric” or “binary” coding.
In thermometric coding, the elementary contributions used for generating the output analog signal assume values identical to one another and are generated by distinct sources numbering N, where N=2n represents the number of levels of the output analog signal for a number of bits equal to n. Optionally, in order to obtain a balanced output analog signal, i.e. an output signal of zero mean value, able to assume either positive values or negative values that are symmetrical with respect to zero, half (N/2) of the elementary sources may be designed for supplying positive elementary contributions and the other half of the sources for supplying negative elementary contributions to the output analog signal. The value of each elementary contribution is 2AMAX/2n, where AMAX represents the maximum amplitude, either positive or negative, that the output analog signal should assume.
Differently, in binary coding, the number of distinct sources to be implemented for providing the elementary contributions is equal to the number of bits n of the digital-to-analog converter that is equal to n=log2N. The dimensions of the integrated elementary sources (e.g. current generators) are not identical but appropriately graded in such a way that the elementary contributions thereby produced are submultiples of a power of 2 with respect to the maximum value AMAX, in which the least significant bit (LSB) has a weight of 2AMAX/2n, while the most significant bit (MSB) has a weight of AMAX.